The present invention relates to a method and apparatus for removing foreign matter, dust, or the like, deposited on a surface of a flexible support (hereinafter referred to as "base film"). That is, the invention relates to a method and apparatus for removing dust from a base film.
The terminology "base film" used in the present invention generally means a flexible belt-like member formed from: a film of resin, such as polyethylene terephthalate, polyethylene-2,6-naphthalate, cellulose diacetate, cellulose triacetate, cellulose acetate propionate, polyvinyl chloride, polycarbonate, polyimide, polyamide, etc., and having a thickness in a range of from the order of microns to the order of tens of microns; paper coated or laminated with .alpha.-polyolefin, such as polyethylene, polypropylene, ethylenebutene copolymer, etc., and having 2 to 10 carbons; foil of metal such as aluminum, copper, tin, etc.; or means a belt-like member in which a pretreated layer is formed on a surface of the above-mentioned flexible belt-like member used as a base material.
Further, the aforementioned base film is treated such that a coating composition, in accordance with the purpose of use, such as a photographic light-sensitive coating composition, a magnetic coating composition, a surface protection coating composition, an antistatic coating composition, a lubricating coating composition, or the like, is applied onto either one or both of the surfaces of the base film, and the thus coated base film is dried and cut into pieces of a desired width and a desired length. Typically the base film may be used for various types of photographic films, sheets of photographic printing paper, magnetic recording media such as magnetic tapes, and so on.
Generally, the base film used for various purposes as described above is subjected to a so-called dust removing treatment, as a pretreatment before the coating treatment, for forcedly removing dust, or the like, deposited on the surface of the base film. As a well-known dust removing method, there are a method of pressing nonwoven fabric, a blade, or the like, against the surface of the base film and a method of blowing out air, having a high-degree of cleanliness, to the base film while ultrasonically or speedily vibrating the air, so that deposits are separated by the air from the surface of the base film and led to a nearby provided suction port. Both of these methods are of the dry type. On the other hand, as a wet type base film dust removing method, known are a method in which a base film is introduced into a cleaning tank and deposits are separated by ultrasonic vibration, or the like, in the cleaning tank, and a method in which a cleaning solution is supplied to a base film, and air is blown and sucked at a high speed to and from the base film. These cleaning methods are effective for removing relatively large-size deposits not smaller than the order of tens of microns or deposits of relatively weak adhesion, but these cleaning methods are almost ineffective for removing small-size deposits or deposits of relatively strong adhesion.
In order to solve those problems, a method has been proposed as disclosed in Japanese Patent Examined Publication No. Hei-5-50419. The proposed method comprises the steps of: applying a solvent (hereinafter a solvent for a concerning purpose is referred to as a "cleaning solvent") onto a base film; and pressing a rod member against the base film which carries the solvent remaining thereon while the rod member is being rotated in a direction reserve to the running direction of the base film so that deposits on the base film are separated and scraped. When the rod member rotating in a direction reverse to the running direction of the base film is pressed against the base film after the cleaning solvent is applied onto the base film, not only a small gap is formed between the base film and the rod member so that deposits which are larger in size than this gap are prevented from passing through the gap but also shearing force is applied on the deposits through the solvent, and the dust-removing effect can be recognized also for smaller-size deposits or deposits of relatively strong adhesion.
On the other hand, with the advance of the density of magnetic recording media, the level of requirements for removal of deposits on the surface of a base film has become further strick so that a method having a higher dust-removing effect has become in demand.
In the case of the aforementioned method of pressing a rod member which is rotating in a direction reverse to the running direction of the base film, for example, the following means is considered as means for improving the dust-removing effect. That is, the curvature of the rod member is reduced to heighten the surface pressure between the rod member and the base film and further reduce the gap between the base film and the rod member so that smaller deposits can be prevented from passing through the gap and strong shearing force can be given to the deposits through the solvent.
Further, as another cleaning method, a method has been proposed as disclosed in Japanese Patent Unexamined Publication No. Sho-62-65872. In the proposed method, a blade having a sharp edge is provided, instead of the rod member rotating in the direction reverse to the running direction of the base film, to heighten the cleaning effect.
These dust removing methods including the step of giving high shearing force, however, have a problem that floating dust, or the like, is again deposited on the base film because the base film is electrostatically charged after the dust removing step. Although a countermeasure of disposing a general destaticizer after the dust removing step, or the like, was generally taken to solve this problem, there arose a new problem that electrostatic charges can not be removed perfectly by such a general destaticizer as the quantity of electrostatic charges increases.